SiRNA has been identified as an important therapeutic agent by its ability to silence proteins with a very high degree of specificity. Naked siRNA is rapidly broken down in the blood and thus many delivery vehicles are been developed to carry it into tumors. The most common lipid agents are however associated with toxicity. In this study we show that pristine single walled carbon nanotubes can be easily complexed to siRNA and serve as non-toxic agents to deliver siRNA into cancer cells and tumors to effectively silence the target.